<p>Integrating and cross-comparing the findings of existing leniency experiments, this paper highlights multiple important experimental phenomena related to the effectiveness of leniency. The information extracted from existing leniency experiments provides useful guidelines for policy-making. In addition, this paper shows that auxiliary experimental settings may subtly influence the experimental results. Importantly, this paper explains that external validity issues are not trivial for the inferences of leniency experiments. Overlooking these external validity issues may lead to underestimation or overestimation of the effectiveness of leniency. Thus, this paper suggests that the interpretation of leniency experiments’ findings and policy recommendations should be based on relevant prior knowledge from other fields, e.g., economics, law, and psychology, as well as the theoretical and empirical studies in the field of leniency. Moreover, future leniency experiments can further enrich the understanding of this topic if existing external validity issues are addressed.</p>